H. JAMES-CLARK ON THE AFFINITIES OF SPONGES. 333 



disc is a sensorial centre, not only for the former but also for the flagellum, which arises close 

 to it, on the ventral side. When we recall instances of the presence of a similar disc, which 

 is unaccompanied by a red spot, in certain species of uniflagellate, natant Flagcllata {Per- 

 anema ? Duj.), and mark how long it is persistent after the body has fallen to pieces for the 

 lack of fresh water, one cannot but feel that its superior consistency is a fair warrant for the 

 belief that it is at least an important organ, and that, seeing the very faint color of that of 

 Astasia trichophora, the absence of all tint does not necessarily exclude it from the category of 

 visual organs. On the other hand, it might be justly questioned whether even the deepest 

 colored spots are at all sensitive to light ; and the only answer would be, that analogy 

 renders it highly probable that they are. 



The mouth (m) is a very marked feature when contrasted with that of other flageMfers. It 

 is usually to be observed in a closed state (fig. 46, m), when it may be recognized as a short, 

 dark, sharply defined double line trending lengthwise with the body, and situated on the 

 ventral side, a short distance behind the base of the flagellum, and just in front of the 

 contractile vesicle. When open it has a more or less broad oblong shape, and is more con- 

 spicuous than when closed. During the introception of food it is quite active, but whether 

 for the purpose of mastication, or merely to manoeuvre the incoming particles, cannot be 

 said positively, although it is probably with the latter design. The peculiar knobbed, parti- 

 colored aspect of the body is due to the almost invariably present large, highly refracting, 

 red and yellow granules in the general cavity. 



The contractile vesicle (cv) is situated just behind the mouth, but near the dorsal side of the 

 body. At full diastole it is globular, and its diameter is one third of the breadth of the 

 region in which it is situated. The systole is abrupt, and appears to be complete ; and 

 the diastole is slow, seeming to occupy all of the intervening time between the systoles. 

 The rate of systole was not ascertained with sufficient accuracy to be recorded, but I should 

 judge it to be not more than four or five times a minute. 



The reproductive organ (n) is probably represented by a very large, light, oval mass which 

 nearly fills the middle of the body. It has a decided outline, and, with the exception of a 

 rather large, central, nucleiform body, its contents are homogeneous. 



§ 13. Anisonema (A. concavum, nov. sp.) 



(Plate X., figs. 65-69.) 



Among all the heteronematous gubernaclifers, Anisonema possesses the highest degree 

 of differentiation in its flagella (fl,fl 2 ) ; for whilst in Heteromita and Heteronema these organs 

 are comparatively more like each other, and arise from a nearly common point, as in the 

 Homoionemata, in the former genus they exhibit a greater diversity of character, and also 

 originate from more widely separated regions. These are particularly observable in the spe- 

 cies before us now, and are certainly more valuable diagnostic characters than the presence 

 of an uncontractile integument by which to distinguish it from its congeners. The habitat 

 of this animalcule is among tangled masses of confervoid Algcc in ponds and ditches, where 

 decaying substances are most abundant. Upon these it moves with a more or less uneven 

 pace ; at one time gliding over a smooth surface with scarcely a perceptible effort, and at 

 another progressing with a laborious, hitching gait, and lashing its guber nudum (/ 2 ) about, 



MEMOIRS BOST. SOC. NAT. HIST. Vol. I. Pt. 3. 8 



